1. Field of the Invention
The subject invention relates to force translating and transducing systems and, more specifically, to methods and apparatus for transducing forces into electric signals.
2. Prior-Art Statement
By way of background, beam transducers are known which employ cantilever structures including thin, delicate pieces of silicon. As apparent from U.S. Pat. Nos. 3,970,982 and 4,051,451, flexible C-shaped members of relatively thin material are employed to transmit forces to the silicon beam. A gross stop member is employed opposite the force transmitting member in the path of the silicon beam as an overload protection.
In practice, it would frequently be desirable to omit the thin, flexible C-shaped member for a tighter coupling of the transducer membrane to the silicon beam. However, this would introduce a non-linear response and potential breakage of the thin, delicate silicon beam in response to larger forces. On the other hand, retention of the thin, flexible force transmitting member would permit sufficient deflection of the transducer diaphragm for permanent deformation, unless a further stop were provided for the transducer diaphragm itself. In addition, the above mentioned gross stop technique introduces a considerable tolerance problem since any beam thickness tolerance may affect the actual amount of possible beam travel relative to the prior-art stop.
The mentioned cantilever beam design has the further disadvantage of providing on either of its two main surfaces only a compression area or then only a tension area at any instant in the operation of the transducer. For the generation of differential transducer signals, it would, therefore, be necessary to provide gage elements on both sides of the beam. In practice, it is, however, very difficult to diffuse gage elements on both sides of a beam of a material such as silicon. A known structure which provides both compression and tension areas on both main beam surfaces is the folded beam. As may, for instance, be seen from Crandall and Dahl, AN INTRODUCTION TO THE MECHANICS OF SOLIDS (McGraw-Hill, 1959), pp. 102 to 104, a folded beam structure is capable of providing oppositely acting moments of force on the same side of the main beam.
Unfortunately, conventional stop member techniques, such as shown in the above mentioned prior patents or in U.S. Pat. Nos. 3,341,796, 3,365,689, 3,377,866, 3,433,064 and 3,537,318 are useless in the cases of folded beam structues. In particular, and unlike a more conventional cantilever beam, an S-bend folded beam cannot be stopped by simply limiting movable end travel, because this would fail to restict torsion due to the folded beam couple. Also, fracture of the thin silicon beam would result if the stop were to contact the silicon beam at its center, or its end, or at any other location.